Experimental and Numerical Studies on Asphaltene Precipitation Distribution during CO2 Flooding in Ultra-Low Permeability Reservoirs

Asphaltene precipitation (AP) is an aspect of serious causes in decrease of production capacity of mature oil fields and is a common phenomenon during CO₂ injection in ultra-low permeability reservoirs. Therefore, there is an urgent need to determine precipitation mechanism, related influencing factors, and possible distribution area.

Laboratory experiments and numerical simulations are conducted to study the influencing factors and distribution mechanism of AP. A visible detection system was employed to obtain the critical pressure and temperature of AP in the CO₂-oil system. Core flooding experiments were designed to study the influencing factors of AP under different pressure and temperature on porosity, permeability, and oil recovery efficiency. Prior to constructing the three-dimensional numerical model, a one-dimensional model is built to fit the core flooding experiments, thereby ensuring accuracy.

The results obtained by experimental studies indicate that the amount of AP increases as the pressure rises to minimum miscibility pressure and then decreases slowly. As the temperature increases, the amount of deposition also increases and then remains almost unchanged. Additionally, the numerical simulation indicates that AP is affected by three main factors: oil components, pressure, and temperature conditions. In turn, AP affects porosity, permeability, and oil recovery.

The encouraging results of the field application effect of deposition distribution prediction based on the numerical model corrected by displacement experiments can enable efficient and referable solutions regarding reduction of AP in CO₂ flooding and improvement in ultimate oil recovery.